1. Field of the Invention
The present invention relates to mobile communication networks, and especially to performance testing in mobile communication networks, for example with 3GPP multicarrier High-Speed Downlink Packet Access User Equipment.
2. Description of the Related Art
The evolution of cellular wireless communication systems has been marked with different generations. 1st generation (1G) included analog systems such as AMPS (Advanced Mobile Phone System) and NMT (Nordic Mobile Telephone) cellular phone networks, introduced in the early 1980s. The second generation (2G) introduced digital cellular telephony such as the GSM (Global System for Mobile Communications) standard, introduced in the early 1990s, which was standardized by the European Telecommunication Standards Institute (ETSI). GSM applies Time Division Multiple Access (TDMA) based radio interface. GSM is still the most widespread standard used in mobile communications.
After the 2G networks, 3rd Generation Partnership Project (3GPP) has standardized globally applicable system specification for 3rd generation mobile communication system. An example of such a system is a Universal Mobile Telecommunications System (UMTS) which applies Wideband Code Division Multiple Access (WCDMA) in its air interface. Original chip rate in WCDMA was specified as 3.84 Mcps and the nominal carrier spacing as 5 MHz. In 3GPP release 5, the concept of High-Speed Downlink Packet Access (HSDPA) has been introduced. It is an enhanced communications protocol in the High-Speed Packet Access family which allows higher data transfer speeds and capacity. With HSPDA, data rates up to 4 Mbps for packet switched data are supported. HSPA+ or “Evolved High-Speed Packet Access” is a subsequent wireless broadband standard, and it was defined in release 7. HSPA+ provides further increase in data rates by using higher order modulation methods (such as 64QAM) and by using multiple antenna techniques such as “multiple-input multiple-output” (MIMO) which means employing several antennas both in the transmitter and the receiver.
In release 8, a concept of Long Term Evolution (3GPP LTE) was introduced. Instead of the earlier WCDMA based radio access technology, Orthogonal Frequency Division Multiplexing (OFDM) is applied in LTE. Also, a dual cell HSDPA (DC-HSDPA) is introduced in release 8 which enables a single user equipment (UE) to receive on two adjacent carriers. Dual cell HSDPA is based on a primary and secondary carriers where the primary carrier provides all downlink physical channels together with channels supporting the uplink data transmission, comprising e.g. a first set of High Speed Physical Downlink Shared Channels (HS-PDSCHs) and High Speed Shared Control Channels (HS-SCCHs). The secondary carrier is responsible for transmitting a second set of HS-PDSCHs and HS-SCCHs. Release 8 allows data rate around 42 Mbps when dual cell functionality is used with 64QAM modulation.
Release 9 combined the dual cell HSDPA with MIMO functionality and also extends the dual cell approach to uplink direction. Furthermore, the used carriers may locate in two separate bands for downlink transmission, providing a dual band HSDPA (DB-HSDPA) operation. Bands can be distant, e.g. dual band configuration no 1 in release 9 is specified to represent downlink bands 925-960 MHz and 2110-2170 MHz. This aspect has great effect on planning the UE's RF parts so that the receiver is able to receive in these two bands simultaneously.
Release 9 has further been developed to a standard named as LTE Advanced, represented by release 10 and fulfilling all 4th generation system requirements. The LTE architecture comprises an Evolved UMTS Radio Access Network, abbreviated by E-UTRAN. Release 10 specifies for HSDPA a use of three or four carriers in the downlink direction. This means the UE can receive on four adjacent carriers each having a 5 MHz band. It will provide even higher data rates; with MIMO this approach makes possible data rates up to 168 Mbps.
3GPP has also specified different release-independent performance requirements for UEs applying the HSDPA. Interference aware receivers are marked with an additional “i”; thus, type 3 is for instance a diversity equalizer and type 3i represents a diversity equalizer with interference awareness. The type 3i receiver takes into account not only the interference arising from users in the serving cell but also the notable interference arising from the other (usually neighbouring) cells.
For example, specification 3GPP TR 25.963 (V9.0.0) discusses a feasibility study on interference cancellation for UTRA FDD User Equipment. It includes general simulation configurations with different type of receivers, interference models and several other parameters for HSDPA traffic, and also it covers type 3i receivers.
There have been discussed test configurations for type 3i receivers where dual cell HSDPA is used. The receiving properties of the receiver with an equalizer, affected by different radio channel conditions, are needed to be tested with a test setup. One such setup is shown in document R5-104591 “DC-HSDPA Type 3i test cases: proposal for simplification”, 3GPP TSG RAN WG R5 Meeting #48, 23-27 Aug. 2010; page 3. This is also shown in FIG. 1. The test setup includes two wanted TX sources 1 and 2 (10a and 10b). Source 1 has carrier frequency f1 and source 2 has carrier frequency f2 which is adjacent with f1. The bandwidth for each carrier is here 5 MHz. A diversity antenna is used, which is shown with two antenna ports (marked Rx) in the UE 17 under test. For the test procedure with antenna diversity, the source signals need to be fed into simulated radio channels 13 but these channels need to have uncorrelated fading with each other. Type 3i receiver requirements include the use of three cells for a single carrier. This can be seen in FIG. 1 by a wanted signal and two interfering signals in both sources. Tx signals are each fed through splitters 11 into an attenuator-fader (12, 13) combination which presents a radio channel which is further uncorrelated with the other radio channels. White noise must also be modelled and fed into the simulation. This is done by Additional White Gaussian Noise (AWGN) blocks 14 fed through respective attenuators 12. Different wanted and interference signal branches are combined through couplers (or “HYB”) 15 and through a directional coupler 16 according to the wirings of FIG. 1. The diversity antenna branches of the UE 17 receive the combined RX signals which are then examined. The other signal direction (uplink) where the UE transmits data, is represented by the directional coupler 16, the lower-most attenuator 12 and the Rx port in the second signal source 10b. 
It is significant that in order to create this test scenario, twelve fader blocks (=channel emulators) and fifteen attenuator blocks are required in order to test the RX properties against DC-HSDPA requirements of the type 3i receivers.
The above mentioned prior art, document R5-104591 mentions an enhanced solution (see page 4 of the document) which depicts the use of six fading channel emulators. It combines each of the similar TX signal types together (e.g. interferer no 1 in the first frequency with the interferer no 1 in the second frequency), directs those signals into two separate faders (bandwidth is 10 MHz), and the resulting components are combined with couplers and added noise (AWGN) to two RX antenna ports. This solution is a little bit simpler than the earlier solution. The problem of this solution which is also mentioned in the document itself is that the fading profiles originally designed for 5 MHz bandwidth are now extended to a 10 MHz bandwidth. Therefore, unwanted periodicity will occur in time domain. Some extension for the 5 MHz bandwidth channel model would thus be needed. Also, it is notable that because of the 10 MHz bandwidth faders, the test setup according to R5-104591 is not applicable to cases where carriers are not configured on adjacent frequencies, such as in dual band dual cell HSDPA systems (DB-DC-HSDPA), see above.
Considering release 10 and its four adjacent downlink carriers in up to two separate bands, in other words in “4C-HSDPA”, 24 pieces of channel emulator blocks are needed, together with 8 pieces of AWGN blocks. Finally, considering the latest 3GPP release 11 concentrating on advanced IP interconnection of services, it would introduce the use of up to eight downlink carriers, thus called as “8C-HSDPA”. This scenario would need 48 fading channel emulators to be used in the performance testing of type 3i receivers.
Due to the above mentioned issues, the inevitable problem of the prior art is complexity of the test equipment which is even emphasized in more sophisticated requirements of the latest 3GPP releases. This also increases the costs of the testing equipment, thus making the prior art approaches very expensive and thus, not sustainable. Therefore, there is an obvious need for simplifying the environment used for the performance testing.